Effects of different analytic systems on the immunophenotypic analysis of peripheral blood lymphocyte subsets by flow cytometry

Objective To investigate the appropriate setting up of normal reference ranges of lymphocyte subsets in some flow cytometry laboratories and to study the effects of different flow cytometers and various reagents by different manufacturers on the analysis of peripheral blood lymphocyte subsets. Methods Three FCM labs (named A, B and C) in Beijing region were selected representing 3 commonly used flow cytometers (Beckman Coulter Epics XL, Beckman Coulter Cytomics FC500, BD FACS Calibur). 50 samples from healthy donors were distributed to 3 labs and tested according to individual lab's standard operating procedure to verify whether the normal reference ranges of peripheral blood lymphocyte subsets established were appropriate. The application of internal quality control was also investigated. Commercial blood quality control reagents were given to the 3 FCM labs and tested within 20 working days paralleled with routine samples. In addition, 20 patients' samples were prepared using 4 different combinations of reagents ( a , b , c and d). The results from combination a, which used the Beckman Coulter reagents and instrument, were compared to the results from combination b, c and d, which used reagents from different manufacturers. Then the prepared samples were tested on Beckman Coulter Epics XL to evaluate the effects of different combinations of reagents on the results of peripheral blood lymphocyte subsets analyzed by the same instrument. Furthermore, 24 patients' samples prepared by same reagents from Beckman Coulter company were tested on both Beckman Coulter Epics XL and BD FACS Calibur respectively to assess the effects of different instruments on peripheral blood lymphocyte subsets. 20 patients' samples prepared by same reagents and instruments were analyzed by Beckman Coulter Epics XL analytic system and BD FACS Calibur analytic system respectively to assess the effects of the two analytic systems on the lymphocyte subsets. Results Over 10% of the results for NK and T4/T8 in lab A as well as T4 in labs B and C fell outside of their normal reference ranges. The probabilities exceeding corresponding normal reference ranges were 16% ( 9/50 ), 24% ( 12/50 ), 22% (11/50) and 12% ( 6/50 ), respectively. The results using internal blood quality control in 3 FCM labs within 20 working days were all within the reference ranges of the quality control provided by the kit. The biases from b and c reagent combinations were substantial compared with that of reagent a combination. Among the biases from b and c reagent combinations, the lowest probability of bias exceeding 10% was T8 of combination b, which had probability of 70% (14/20). The highest probabilities of hias exceeding 10% were T3 and T4 of b and c reagent combinations, which reached 100% (20/20) . Furthermore, the biases of T3, T8 and B of d reagent combination compared with that of reagent a combination were also substantial. The probabilities of bias exceeding 10% were 35% (7/20) ,85% (17/20) and 75% (15/20), respectively. Comparing the results of samples prepared and analyzed by reagents and instruments from different manufacturers to that of samples prepared and analyzed by the same company's reagents and instruments showed that there were great discrepancies in T3, T4 , T8 , B and NK. The probabilities of bias exceeding 10% were 71% ( 17/24), 80% (19/24) ,38% (9/24), 33% (8/24) and 92% (22/24), respectively. The biases of T8, NK and B were substantial when compared the results from Beckman Coulter Epics XL analytic systems and BD FACS Calibur analytic systems. The probabilities of bias exceeding 10% were 55% (11/20 ), 70% ( 14/20 ) and 55% (11/20), respectively. Conclusions FCM labs should set up their own normal reference range for peripheral blood lymphocyte subsets. The normal reference range should be verified periodically. It is important to apply internal blood quality control regularly and accumulate the quality control results. The reagents and instrument for preparing peripheral blood samples should be from the same manufacturers. Key words: Flow cytometry;  Lymphocyte subsets;  Reference values;  Quality control